Electromagnetic compatibility (EMC) is a fundamental constraint that all electric or electronic equipments must meet to ensure the simultaneous operation of electric or electronic devices present at the same time in a given area, for a given electromagnetic environment.
By definition, EMC covers two complementary aspects: the electromagnetic (EM) emission and the immunity to electromagnetic interferences. When designing new electric or electronic devices, it is desirable to both keep the emission low and ensure robustness of the device, such that it complies with certain limits. Mainly, such EMC limits are defined by standards, e.g. CISPR 25, “Radio disturbance characteristics for the protection of receivers used on board vehicles, boats, and on devices—Limits and methods of measurement”, IEC, 2002. Sometimes, more drastic limits may be defined by the customers. Moreover, the measurement equipment is described in CISPR 16-1-1 Specification for radio disturbance and immunity measuring apparatus and methods—Part 1-1: Radio disturbance and immunity measuring apparatus—Measuring apparatus.
When the maximum level of EM emissions at a given frequency specified by a standard or by customers is exceeded, the performance can be improved by spreading the signal at a specific frequency over a band of frequencies. Indeed, frequency spreading is often used to reduce the susceptibility of a receiver to an aggressor or to reduce the effect of a transmission on a victim.
The measurement of electromagnetic emissions by hardware can only be carried out on a real device, e.g. aprototype, and not during the design phase. The difficulty is to determine the optimum parameters for the frequency spreading, which may include the form of the modulating signal (ramp, triangle, stepped or linear, etc), the frequency of the modulating signal and the peak frequency deviation, without having to spend time simulating “real schematics” or, worse, having to generate numerous versions of the device to test different configurations.
Key principles of frequency spreading applied to EM emission reduction, as well as more general considerations regarding frequency spreading are disclosed in the publication by J. Shepherd, et al, “Getting the most out of frequency spreading”, EMC Compo 2009.
However, the addition of the frequency spreading function into the existing schematic of the device under test (DUT) may be difficult to achieve, particularly when various combinations of frequency spreading parameters must be tried.